title: Adjustment to the light environment in small-statured forbs as a strategy for complementary resource use in mixtures of grassland species.
abstract: OBJECTIVE
  The biological mechanisms of niche complementarity allowing for a stable coexistence of a large number of species in a plant community are still poorly understood. This study investigated how small-statured forbs use environmental niches in light and CO(2) to explain their persistence in diverse temperate grasslands.
  
  
  METHODS
  Light and CO(2) profiles and the corresponding leaf characteristics of seven small-statured forbs were measured in monocultures and a multi-species mixture within a biodiversity experiment (Jena Experiment) to assess their adjustment to growth conditions in the canopy.
  
  
  RESULTS
  Environmental conditions near the ground varied throughout the season with a substantial CO(2) enrichment (>70 µmol mol(-1) at 2 cm, >20 µmol mol(-1) at 10 cm above soil surface) and a decrease in light transmittance (to <5 % deep in the canopy) with large standing biomass (>500 g d. wt m(-2)) in the multi-species assemblage. Leaf morphology, biochemistry and physiology of small-statured forbs adjusted to low light in the mixture compared with the monocultures. However, the net carbon assimilation balance during the period of low light only compensated the costs of maintenance respiration, while CO(2) enrichment near the ground did not allow for additional carbon gain. Close correlations of leaf mass per area with changes in light availability suggested that small-statured forbs are capable of adjusting to exploit seasonal niches with better light supply for growth and to maintain the carbon metabolism for survival if light transmittance is substantially reduced in multi-species assemblages.
  
  
  CONCLUSIONS
  This study shows that adjustment to a highly dynamic light environment is most important for spatial and seasonal niche separation of small-statured forb species in regularly mown, species-rich grasslands. The utilization of short-period CO(2) enrichment developing in dense vegetation close to the ground hardly improves their carbon balance and contributes little to species segregation along environmental niche axes.
authors.affiliation: UFZ, Helmholtz Centre for Environmental Research, Department of Community Ecology, Theodor-Lieser-Strasse 4, Halle, Germany. christiane.roscher@ufz.de
authors.forename: Christiane
authors.initials: C
authors.lastname: Roscher
authors.forename: Werner L
authors.initials: WL
authors.lastname: Kutsch
authors.forename: Olaf
authors.initials: O
authors.lastname: Kolle
authors.forename: Waldemar
authors.initials: W
authors.lastname: Ziegler
authors.forename: Ernst-Detlef
authors.initials: ED
authors.lastname: Schulze
mesh_terms: D000222:Adaptation, Physiological; D044822:Biodiversity; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism; D004777:Environment; D008027:Light; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D010944:Plants / Q000378:metabolism*; D006109:Poaceae / Q000502:physiology* / Q000528:radiation effects; D011157:Population Dynamics; D012621:Seasons; D013227:Steam / Q000032:analysis
chemical_list: D013227:Steam; D002245:Carbon Dioxide